GENKI is the most popular Japanese learning textbook which published by The Japan Times. GENKI is
It's an integrated textbook series in elementary Japanese which is utilized college, high schools over the world. Develops the skill of speaking, listening, reading and writing. Effectively to learn!
Two volumes, 23 lessons approx. 300 kanji, 1100 vocabulary. Estimated 200 hours to complete.
Official site: http://genki.japantimes.co.jp/index_en
​Here you can buy GENKI series direct fromAmazon Japan to save your money.